Given the demanding nature of many professions, efforts are ongoing to develop initiatives to improve occupational wellbeing, including mindfulness-based interventions (MBIs). To assess the efficacy of MBIs, meta-analytic procedures were conducted on 35 randomized controlled trials derived from an earlier inclusive systematic literature search (covering all occupations, MBIs, and wellbeing-related outcomes). Mindfulness had moderate effects on deficit-based outcomes such as stress (SMD = −0.57), anxiety (SMD = −0.57), distress (SMD = −0.56), depression (SMD = −0.48), and burnout (SMD = −0.36), and moderate to small effects on asset-based outcomes like health (SMD = 0.63), job performance (SMD = 0.43), compassion and empathy (SMD = 0.42), mindfulness (SMD = 0.39), and positive wellbeing (SMD = 0.36), while no effects were observed for emotional regulation. However, the quality of the studies was inconsistent, suggesting more high-quality randomised controlled trials are needed.